Gas turbine engines include a plurality of airfoils disposed circumferentially around the perimeter of a rotor disk. For optimum performance, it is ideal that the airfoils be light weight and stiff, because, during gas turbine engine operation, the rotating airfoils are often subject to a variety of different forces. For example, the airfoils typically experience centrifugal forces, aerodynamic forces and vibratory stimuli due to the rotation of the airfoils over the various operating speeds of the engine. One conventional way to reduce weight from the airfoil is to create pockets within the airfoil and to fill those pockets with a suitable light weight filler material for completing the aerodynamic profile of the airfoil. The pockets, however, reduce the stiffness of the airfoil. As such, the dovetail root and transition portion of the airfoil are often times solid in order to maintain stiffness in these critical areas.
A creative way to eliminate additional weight from the dovetail root and transition portion of the airfoil without negatively affecting stiffness much is to drill cavities into the base of the dovetail root. During assembly and disassembly of these airfoils from the gas turbine engine, however, the cavities in the base of the dovetail root cause scratching damage to the dovetail slot. Furthermore, the cavities in the base of the dovetail root have the potential to ingest water and other foreign objects during engine operation. If water gets into the cavities, the water has the potential to freeze and create an imbalance in the gas turbine engine due to the fact that not all the airfoils in the rotor disk may have ingested water. This potential imbalance can adversely affect the engine performance and must be avoided to maintain the efficiency of the engine.
Accordingly, there is a need to provide a light weight airfoil that maintains stiffness, avoids damaging other components of the gas turbine engine during assembly and disassembly, and prevents engine imbalance due to foreign object ingestion into lightening cavities of the airfoil.